Functionally different T lymphocyte subpopulations determined by their sensitivity to complement-dependent cell lysis with the monoclonal antibody 4A.

A human T lymphocyte antigen 4A (40,000 daltons) is defined by a monoclonal, complement- (C) fixing, hybridoma-produced antibody (moAb 4A). This antigen, which is identical to the previously reported antigen 3A 1, is expressed at quantitatively different levels on functional subsets of peripheral T lymphocytes as determined by the cell sensitivity to antibody and C. Peripheral T lymphocytes can be divided into two populations: 4A high-density T cells (4A increases), which are killed in vitro by moAb 4A + C, and 4A low-density T cells (4A decreases), which are not affected in vitro by moAb 4A + C treatment. The helper/inducer T cell lineage, defined by moAb Leu 3a, and the cytotoxic/suppressor T cell lineage, defined by moAb Leu 2A, contain both 4A increases and 4A decreases T cell populations. Functional studies by moAb 4A + C treatment show that 1) the 4A increases T cell population contains T helper cells, which are necessary for in vitro antibody production against red cell-bound determinant; 2) the 4A decreases T cell population contains the precursor T cells, which proliferate in vitro in MLC, and the precursor T cells, which are necessary for the in vitro generation of the alloreactive cytotoxic T cells; and 3) the cytotoxic activity of alloreactive T cells generated in CML assay is abrogated by moAb 4A + C treatment; 4) the activation of T cells by PHA and Con A increases the quantitative expression of 4A antigen.